MICROphysicS of COnvective PrEcipitation (MICROSCOPE)

Abstract

This project will improve predictions of severe convective rainfall by addressing the problem of the microphysicsof precipitation in convective clouds. For the first time, study of the microphysics is embedded in aproject that includes the larger-scale dynamics of convective clouds, as part of the COnvective PrecipitationExperiment (COPE). COPE will connect this microphysical study with the system-scale dynamics of severeconvective UK weather events. COPE will also provide a programme of weather-system modelling, which willbring the microphysical understanding through to the improved prediction of rainfall at the weather-system, orcatchment scale.

Weather forecast models are now run at resolutions of 1.5 km, which has helped to improve the predictionof the location and timing of convection. However, quantitative precipitation forecasts are still often poor ashighlighted in the Boscastle event (Golding et al., 2005). This is due in part to the lack of knowledge about thenucleation of ice particles in convective clouds, the warm rain process, and the rates of production of secondaryice particles and the subsequent growth of precipitation particles. However, high local accumulations were theresult of both intensity (microphysics of precipitation) and duration (organisation of and interaction between cellsalong the convergence line) of precipitation. The latter issue and wider-scale problem will be addressed in otherparts of COPE.

There are two key parts to MICROSCOPE. The first concerns a fundamental problem: how do ice particlesform in clouds as a result of ice nuclei (IN), particularly at high temperatures? The second concerns precipitation:how do precipitation particles form and what are the rates of production and development? MICROSCOPE willaddress the challenge of explaining the production of primary ice particles in cumulus clouds, in the followingways.* We will make measurements of the properties of the aerosol particles, particularly soils and biologicalmaterial, on the ground and in the boundary-layer with the FAAM 146 aircraft.* Measurements will be made of the evolution of the droplet size distribution, the possible presence ofsupercooled raindrops and the formation of the first ice particles with carefully-guided penetrations of theaircraft that has been equipped with new instruments that can detect and characterise small ice particlesunambiguously (SID, 2DS, CAS-DPOL).* The dual-polarisation, Doppler radars will provide measurements of the location and time of the first precipitationechoes, the air motions and the types of particles.

In order to explain the production and development of precipitation, process model and NWP model resultswill be compared to observations of the entrainment process, the development of the warm rain process, thegrowth of ice particles into precipitation particles by diffusional growth, the freezing of raindrops into graupelparticles, multiplication by secondary production processes, and riming. The comparisons will be achieved bymaking multiple penetrations at increasing altitudes measuring the particle size distributions in space and timeas well as the thermodynamics and dynamics of the cloud, and by obtaining information about the particles andthe rate of increase of the reflectivity echo from the dual-polarisation radar.

The final step of MICROSCOPE, that will be led by the Met Office, is to incorporate the new information intoNWP models and to test against the data gathered during the project.

Planned Impact

The research proposed in MICROSCOPE will potentially have a majorbenefit to society and business in the UK by improving weather forecastsof heavy convective rainfall through it's major contribution to COPE.Lives may be saved in severe events if sufficient warning is given.Improved forecasts of flash flooding will also provide greater warningto businesses so they may be able to take action to save loss of stock.Thus, it is likely that the Insurance Industry will be the biggestbeneficiary.

Flooding caused by heavy convective rain is a serious problem in the UKand in the rest of the world. Every year there are reports throughoutthe world of major flooding with significant damage and even loss oflife. There are many examples in the UK, such as Boscastle in 2004 andOttery St Mary, 2008. The Cabinet Office regards flooding as one of themajor risks to public wellbeing. The Pitt Review, written following the2007 floods in the UK, stressed the need for better analysis andforecasting of storms and specifically the need to improve forecastingskill of heavy precipitation events that lead to flooding. The reviewled directly to the setting up of the joint Environment Agency / MetOffice National Flood Forecasting Centre which uses rainfall forecastoutput from the UM as input to the national Grid-to-Grad hydrologicalforecasting model.

NERC recently funded a consortium proposal to investigate the initiationof convective storms in the UK: the Convective Storm Initiation Project(CSIP). This project had a significant impact on the ability of the MetOffice to forecast convective precipitation. It did this by providingthe information that allowed the Met Office to have confidence in ahigher-resolution model. However, the project did not address the issueof the quantity of precipitation. That is the subject of MICROSCOPE.The observations made in MICROSCOPE will provide much needed data withwhich to compare results from the high-resolution Met Office UnifiedModel (UM). Incorporation of research results from MICROSCOPE intodevelopment versions of the UM will be made possible through workingwith Met Office. In turn, the MO forecasts will feed into models usedby EA and SEPA.

A second group that will benefit from MICROSCOPE within the context ofCOPE is the water companies and hydrometeorological consultancies. Theyregard precipitation forecasts as an essential element in their businessoperations.

A major indirect benefit to society as a whole is likely to come fromimprovements made to global climate models that will result fromknowledge gained about the ice processes in clouds as well as theentrainment process. Convective clouds and their influences, such asthe vertical transport of heat, moisture and momentum, the effects onlatent and radiative heating, and the chemical processes due tolightning, are particularly difficult to capture in these models.

Weather forecasts are also an essential element in forecasting the onsetand spread of both human and animal diseases. Work is being carried outwith the National Health Protection Agency on the relationship betweenthunderstorms and outbreaks of asthma, for example.

Finally, this research offers the opportunity to work with schools onoutreach activities, particularly since thunderstorms are so dramaticand appealing to children and the public in general.

The origin of the formation of the ice phase in summer time convection over the SW Peninsula of the UK has been identified along with its role in precipitation formation. The role of atmospheric aerosol in both the warm rain and ice processes has been quantified

Exploitation Route

Continued modelling work but results are not ready yet for wider dissemination

Sectors

Education,Environment

Data

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